The invention relates generally to the field of power over local area networks, particularly Ethernet based networks, and more particularly to a method of notifying a user of a powered device of an excess power demand condition.
The growth of local and wide area networks based on Ethernet technology has been an important driver for cabling offices and homes with structured cabling systems having multiple twisted wire pairs. The ubiquitous local area network, and the equipment which operates thereon, has led to a situation where there is often a need to attach a network operated device for which power is to be advantageously supplied by the network over the network wiring. Supplying power over the network wiring has many advantages including, but not limited to; reduced cost of installation; centralized power and power back-up; and centralized security and management.
Several patents addressed to this issue exist including U.S. Pat. No. 6,473,608 issued to Lehr et al., whose contents are incorporated herein by reference, U.S. Pat. No. 6,643,566 issued to Lehr et al., whose contents are incorporated herein by reference, and U.S. Pat. No. 6,115,468 issued to De Nicolo whose contents are incorporated herein by reference. Furthermore a standard addressed to the issue of powering remote devices over an Ethernet based network has been published as IEEE 802.3af-2003, whose contents are incorporated herein by reference.
A basic issue in remote powering of devices is the need for the power sourcing equipment (PSE) to have sufficient power to operate each powered device (PD) attached to the network. A further issue, as a result, is the necessity of prioritizing power allocation in the event that multiple PDs are connected having power demands in excess of the power sourcing ability of the PSE. In such a circumstance certain PDs will not receive power, however no recommendation in the above mentioned IEEE 802.3al-2003 standard is addressed to notifying the PD, or the user at the remote location, of the excess demand condition. Such a situation may lead to confusion, as the user plugging in the device, which in one embodiment is an Internet protocol (IP) telephone, is unaware of the excess demand condition and may assume that the device is faulty. This leads to unnecessary service calls, and general dissatisfaction with the operation of the network and its associated devices.
U.S. patent application Ser. No. 10/253,800 by LeCreffet al., published as US 2003/0072438 and EP 1,303,078 proposes that when the Ethernet equipment will be unable to supply the required power to the equipment, the Ethernet equipment will send via the line a specific signal notifying the equipment of the incapacity to be remotely powered. Such a device assumes that the PD can operate at some limited functionality in the absence of power from the PSE to notify the user of the alarm signal. Such a requirement increases the cost of the PD. Furthermore, if the initial alarm notification is unnoticed by the user, no mechanism exists to notify the user on a continuing basis of the excess demand condition.
It would therefore be desirable to have an apparatus for, and a method of, notifying an end user at a remote PD of an excess demand condition. Preferably, the notification is operable in the absence of any other power source for the PD. It would also be desirable to have an apparatus for, and a method of, periodically notifying the end user of the excess demand condition